In foundry installations, molten metal may be handled by various devices, some of which are disclosed in U.S. Pat. Nos: 2,264,740 (Brown); 2,333,113 (Martin et al.); 3,395,840 (Gardner); 3,549,061 (Piene); 3,801,083 (Mantey et al.); 3,848,072 (Dershem et al.); 4,638,980 (Beele); and 4,953,761 (Fishman et al.); U.S. Patent Application Publication No. 2010/0282784 A1 (Pavia et al.); and U.K. Patent Application Publication No. GB 2,229,384 A (Fishman et al.).
In such foundry installations, molten metal is frequently poured from a rectangularly-shaped, or otherwise flat bottom holding box into a casting mold. The holding box has a bottom region commonly housing a single nozzle that controls the outward flow of the molten metal. The holding boxes for pouring molten metal are sometimes referred to as ladles, and comprise a substantially enclosed container having a single bottom pour spout commonly controlled by a stopper rod extending vertically through the molten metal in the box. U.S. Patent Application Publication No. 2010/0282784 A1 discloses the use of dual nozzles in a launder. Controlling the flow of the molten metal from the ladle or box to the casting molding is extremely important for successful molding of metal parts. In addition, maintaining the temperature of the nozzle so that it corresponds to approximately that of the molten metal is an important aspect of an efficient pouring process. Further maintaining the liquid, molten state of the metal is also an important consideration, especially when the pouring process encounters unexpected interruptions that may last for a relatively long duration.
As a general rule the flow rate of molten metal being poured from a rectangular box is directly proportional to the square root of the height of the molten metal in the box. This height is commonly referred to as being the “head” parameter. The head parameter (H) directly controls the flow rate (Q) related to the box and both are interrelated by the following relationship:Q∝√{square root over (H)}  [expression (1)]
where Q is equal to the flow rate of the molten metal being poured from the box, and H is equal to the head of molten metal within the box.
The amount of the molten metal that is poured at the flow rate (Q) of expression (1) is also dependent on the volume of the molten metal within the box itself. This volume (equal to the product of L×W×H) is determined by the length (L) and width (W) dimensions of the box, which remain constant. Further, this volume is also dependent upon the height or head parameter (H) of the molten metal in the box. Since the length and width dimensions of the box remain constant, as the head parameter (H) decreases so does the volume (V) of the molten metal within the box, as well as the flow rate (Q). In fact, this relationship dictates that a 75 percent drop in the volume of molten metal contained with a rectangularly-shaped box corresponds to a 75 percent drop in the head parameter (H) and about a 50 percent drop in the flow rate (Q). It is desired that means be provided to yield a flow rate (Q) that is not so directly dependent upon the head parameter (H) when dual nozzles are utilized in a molten metal holding and pouring box having a pyramidal-shaped lower section.
It is desired that a pouring box be provided with means that provide a relatively constant flow of molten metal exiting from the box through a pair of nozzles and being received by a pair of adjacent casting molds. Such a provision allows for the use of dual nozzles having small openings so as to reduce slag formation that would otherwise contribute to the clogging of the nozzles. This constant flow also contributes to the successful molding of metal parts.
Conventional pouring boxes can suffer nozzle clogging problems due to a drop in nozzle temperature during non-pouring delay periods. These delay periods normally occur as the pouring of the molten metal, between the box and the casting molds, is interrupted so as to accommodate sequential mold casting. As the nozzle begins to cool during these sequential delay periods, liquefied slag contained in certain molten metals, as well as the metals themselves, tends to freeze to the inner surface of the pouring nozzle, ultimately leading to clogging of the nozzle.
A further clogging problem can occur because a conventional pouring nozzle may be made of a refractory material and have a construction that comes into contact with both the outer steel shell and a reinforcing plate located around the nozzle of the pouring box. This contact causes the outer shell and the reinforcing plate, both commonly being metal, to act as heat sinks which draw away heat from the pouring nozzle, and thereby decrease the temperature of the nozzle. These heat sink problems may be compensated for by providing a continuous flow of molten metal into the nozzle which counterbalances the removal of heat by the sinks. However, if the pouring of molten metal is not continuous, such nozzle construction leads to the creation of different temperatures along the nozzle which disadvantageously subjects the nozzle to a cooling effect that contributes to clogging.
It is desired that a pouring box with a pyramidal-shaped lower section be provided which has dual nozzles maintained in a heat exchange relationship with the molten metal so as to provide for a constant temperature of the nozzle. Such a construction allows the pouring nozzles to remain at a temperature close to the molten metal in the box, and effectively negates any cooling effect encountered from external devices that would otherwise contribute to clogging problems.
Two (or dual) bottom nozzle pouring boxes can be utilized in mold casting lines where two molds, in-line (in tandem) or side-by-side, are filled with molten metals at the same time. Two individual nozzles 20, as shown, for example, in FIG. 7 may be provided through separate fixed nozzle openings in the bottom of the pyramidal-shaped low section of the box. However this is not preferred since the nozzles will be a fixed distance apart while the distance between sprue cups in a casting line may change. Further replacement of two individual nozzles is time consuming and difficult particular since the change in nozzles is accomplished while the box is extremely hot. Although hot molten metal is drained from the box before nozzle replacement, it is not generally feasible to wait for the box to cool down to around normal room temperature.
It is one object of the present invention to provide a replaceable single (unitary) dual (twin) nozzle (block) assembly in a molten metal holding and pouring box having a pyramidal-shaped lower section that is capable of accommodating casting lines where the distance between the sprue cups of the two molds that are being filled with molten metal flowing through the two nozzles can change.
It is another object of the present invention to provide a replaceable unitary dual nozzle assembly in a molten metal holding and pouring box having a pyramidal-shaped lower section that is more easily replaced than two separate nozzles.
It is another object of the present invention to provide a molten metal holding and pouring box having a pyramidal-shaped lower section with dual pouring nozzles formed from an interchangeable unitary dual nozzle assembly where the spacing between the pair of nozzles in the assembly can be changed based on the selection of a nozzle casting having the same overall dimensions, and where such a molten metal holding and pouring box can be used in combination with two separate stopper rod positioning and control apparatus independently controlling flow from each of the two nozzles in the assembly.